I am having this problem...went to open one of my chicken houses and found 8 purebred hens dead! ALL with their heads off of their necks bitten, nothing else touched. We sat out that night and saw a Fishers Cat (weasel) sneaking back to that house and shot at it but missed. Apparenty they dring the blood from live chickens and are just the meanest animals, will even kill cats, dogs, groundhogs, squirrels (I notice I don't have any more squirrels around either).
Sat out for the last 5 nights and while we were watching one coop it came and killed everything in two others on two different nights. My chicken houses are built like Ft. Knox, with concrete under the doors or raised floors, but weasels just need a tiny space, 3-4", to get in! I am SICK. It seems to only like live chickens, have had no luck trapping with a dead chicken but this thing has to go or we will not have any chickens soon.
Last night it got all my beautiful 2 year old Buff Orpington hens!!